Detection and correction of current transformer saturation effects in secondary current signals

Ideally a current transformer transduces the primary current linearly. In reality the transmission behaviour is non-linear at very high primary currents or at high burden i. e. the current transformer saturates. If saturation takes place the measured secondary current signals are distorted so that protection devices operate delayed or blocked (e. g. differential protection). For post processing issues of the recorded secondary signals one needs to correct the current waveforms. This paper presents a combined and robust method for detection of current transformer saturation effects even for low sampling frequencies. If saturation is present in the analysed current waveform a curve fitting algorithm is used to correct and estimate the unsaturated secondary current. All proposed methods do not require any electrical parameters of the current transformer. The proposed methods are tested on simulated disturbance records and the results are presented in this paper.